West : On Mosses, 



183 



central cell whose protoplasm contracts and forms an oosptiere ; 

 above this a row of cells passes up the axis of the flask-shaped neck 

 of the archegonium, and is continued as far as some cells which form 

 the " stigma " of some writers. This axial row of cells breaks up 

 and is transformed into mucilage before fertilisation, this mucilage 

 swells and forces apart the four stigmatic cells, and forms an opening 

 for the passage of the antherozoids to the oosphere. In the thalloid 

 hepaticae the sexual organs arise below the point of apical growth, 

 from the prostrate thalloid stem or the superficial cells of the thallus, 

 or in marchantiacese on specially metamorphosed branches. In the 

 mosses and the leafy Jimgermannia the archegonia and antheridia may 

 be formed from the apical cell, the latter ones from its last segments, 

 and this is probably the case in Sphagnum. Antheridia and archegonia 

 are generally produced in numbers in close proximity, and are usually 

 enveloped by later outgrowths of the thallus in the thalloid hepaticse, 

 but in the leafy Jungermannia and in mosses several archegonia are 

 surrounded by a perichsetium formed of leaves ; a male flower in 

 mosses is generally formed thus, while the antheridia of Sphagnum 

 and Jungermannia stand alone. There is also a so-called perianth 

 round the archegonium in hepaticae, but not in mosses. The asexual 

 generation or sporogonium arises in the archegonium from the 

 fertilised oosphere or oospore. An egg-shaped embryo is formed by 

 continued cell-division, growing towards the neck of the archegonium. 

 Its final form varies, for in Riccia (the lowest type) it is a globe, the 

 outer cell forming the wall, the inner cells becoming spores ; but in 

 all other cases differentiation takes place into a seta penetrating the 

 bottom of the archegonium and the underlying tissue, and a capsule 

 or theca turned towards thB^^ck of the archegonium. The neutral 

 portion of the archegonium continues to grow when the sporogonium 

 is developing, and finally becomes the calyptra enclosing the sporo- 

 gonium. In Riccia the sporogonium remains enclosed in the calyptra, 

 but in the remaining hepaticce it protrudes after the ripening of the 

 spores by a sudden prolongation of the stalk, when it ruptures the 

 capsule and disseminates the spores, which are mixed with elaters, 

 the calyptra remaining at the base of the seta as a cup-like mem- 

 branous structure. Now in mosses the sporogonium takes a spindle- 

 like shape, and before it develops into a capsule, it detaches the 

 calyptra at its base by upward pressure, and the seta penetrates the 

 tissue of the stem, by which it is surrounded as a sheath, called the 

 vaginula. The spores of the Muscinece, except in Archidium, arise in 

 fours, the mother-cells showing a rudimentary division into two, 



